This dataset provides clay mineral assemblages of marine sediments over the past 5.4 ka at Core SUT10 in the Gulf of Thailand. The data include clay mineral assemblages (smectite, illite, chlorite, and kaolinite), illite chemistry index, and illite crystallinity. The Core SUT10 (10.46°N, 100.92°E; 62 m water depth, 1.51 m long) was retrieved from the cruise of Hydrographic and Oceanographic Survey (HOS) in March 2011. The clay mineral (1-cm resolution, 144 samples) was identified on oriented mounts of non-calcareous, clay-sized (<2 μm) particles by X-ray diffraction (XRD) using a PANalytical X'Pert PRO diffractometer. Replicate analysis of selected samples gave a precision of ±2% (2σ), and the semi-quantitative evaluation of each clay mineral has an accuracy of ~5%. All tests were analyzed at the State Key Laboratory of Marine Geology, Tongji University (Shanghai).